Perhaps Mumble's "killer app" feature is positional audio. When playing supported games, Mumble links with the game’s memory or API to determine where a player is located.
However, 1.3.4 will likely remain the "stable gold standard" for enterprises and gaming clans until 1.4.0 exits beta. For many, the risk of bleeding-edge bugs outweighs the benefits. mumble 1.3.4